Full length active α1 proteinase inhibitor (α1PI, α1 antitripsin) is composed of 394 amino acids (aa) having a mass of approximately 55 kDa when fully glycosylated (Berninger, 1985). Hepatocytes are the primary source of α1PI, and in normal, healthy individuals, the range of circulating α1PI is 20-53 μM between the 5th and 95th percentiles (Brandy et al., 1991; Bristow et al., 1998). However, during the acute phase of the inflammatory response, α1PI may increase as much as 4-fold to 200 μM (Kushner, 1982). There are four common alleles of α1PI, and these are synthesized and secreted principally by hepatocytes (OMIM, 2000). However, there are more than a hundred genetic variants, some of which produce a molecule that prohibits secretion, and affected individuals manifest with 10-15% of the normal level of α1PI in blood (Berninger, 1985). Individuals with this inherited form of α1PI deficiency, especially males, are notably susceptible to respiratory infections and emphysema, and 80% who survive to adulthood succumb to respiratory failure between the fourth and sixth decades of life (Berninger, 1985). Prevalence is 0.03%, and α1PI augmentation therapy in affected individuals is the only approved therapeutic application of α1PI. (OMIM, 2000).
Traditionally, α1PI has been characterized as a proteinase inhibitor which has highest affinity for soluble granule-released elastase (HLEG). Evidence now suggests α1PI also interacts with cell surface HLE (HLECS) (Bristow et al., 2003; Tavor. S. et al., 2005). Both HLECS and HLEG are synthesized and processed as a single molecular protein; however, HLE is targeted exclusively for the cell surface early in ontogeny and for granule compartmentalization later in ontogeny (Gullberg et al., 1995; Garwicz et al., 2005). Mutations in the HLE encoding gene that result in decreased HLE expression produce periodic cycling in hematopoiesis that affect monocytes in the opposite phase to neutrophils (Horwitz et al., 1999; Horwitz et al., 2004). Mutations that result in increased HLE produce twice fewer absolute numbers of circulating CD4+ and CD8+ lymphocytes, and 7 times more monocytic cells (Person et al., 2003).
The proteinases and proteinase inhibitors that govern cell motility and hematopoiesis have evolved a different functional pattern in mice from man, but there are many parallels. For example, in mice, it has been shown that high concentrations of HLE accumulate in bone marrow following granulocyte colony-stimulating factor (G-CSF) induced stem cell mobilization (Winkler et al., 2005). This accumulation was found to result from the down-regulation of α1PI expression. In man, the liver is the primary source of both α1PI and stem cells. As opposed to its function to inhibit the enzymatic activity of HLEG, α1PI binding to HLECS induces cell migration in a manner that does not appear to involve enzymatic activity (Wolf et al., 2003). The effect of α1PI on cell motility is especially profound during migration of stem cells and early progenitor cells. Hematopoiesis begins with stem cell migration from fetal liver through the periphery to the stromal area of hematopoietic tissue, retention, differentiation, and release of maturing progenitor cells back into the periphery. Migration of stem cells to, and myeloid-committed progenitor cells from bone marrow is controlled by HLECS, the chemokine stromal cell-derived factor-1 (SDF-1), and the SDF-1 receptor CXCR4 (Tavor. S. et al., 2005; Lapidot and Petit, 2002). Cell migration is dependent on the localization of HLECS into podia formation at the leading edge of the cell (Tavor. S. et al., 2005; Cepinskas et al., 1999), and podia formation is induced by binding of active α1PI to HLECS in a manner that includes co-localization of HLECS with CD4 and CXCR4 (Bristow et al., 2003). The current method for therapeutic mobilization of myeloid-committed progenitor cells from bone marrow is by the action of G-CSF, and it has been shown that G-CSF mediates this activity by antagonizing CXCR4 and HLECS (Lapidot and Petit, 2002). The molecular mechanisms that mobilize lymphoid-committed progenitors from hematopoietic tissue are not known. Evidence described in this application now suggests active α1PI mediates this activity (Examples 1-3 below). Following treatment with α1PI in animal models, the migration of transplanted human leukemia cells into circulation is decreased, but the migration of stem cells to hematopoietic tissue is increased (Tavor. S. et al., 2005). These results suggest that α1PI influences the migration of cells into and out of circulation depending, in part, on the stage of differentiation of the cell.
When bone marrow-derived erythroid progenitors cells (burst-forming units-erythroid) are incubated with α1PI in vitro, growth of immature cells is significantly suppressed (42.5%±5.5%) (Graziadei et al., 1994). In contrast, growth of mature cells is unaffected by α1PI (3.6%±3.4%). These results demonstrate that in addition to myeloid- and lymphoid-committed progenitors, α1PI influences the genesis of erythroid-committed progenitor cells dependent on their stage of differentiation.
Previous therapeutic application of α1PI has been restricted to augmentation in patients diagnosed with inherited α1PI deficiency for the purpose of ameliorating respiratory distress such as occurs in emphysema and chronic obstructive pulmonary disease (COPD). Considerable interest in producing recombinant α1PI has resulted in development of several successful expression systems including bacterial and plant cell expression as well as viral vector and oral delivery (Chowanadisai et al., 2003; Luisetti and Travis, 1996). Recombinant α1PI is in phase I clinical trials for augmentation in individuals with inherited α1PI deficiency (Flotte et al, 2004), and is in phase II clinical trials for treatment of atopic dermatitis. Recombinant α1PI has been tested for preventing the onset of type I diabetes in genetically predisposed mice (Song et al., 2004). Nevertheless, there is a need in the art for developing recombinant α1PI with due consideration of its conformation-dependent function to mobilize either lymphoid-lineage or myeloid-lineage maturing cells. As recognized by the inventor herein, because α1PI induces cell motility depending on its active or proteolytically modified conformation, various active and modified α1PI's provide powerful new therapeutics for mobilizing targeted cell subsets through tissue.